Aerospace vehicles have many components that are subjected to high thermal and mechanical loading. For example, as a hypersonic vehicle travels through the earth's atmosphere, the high local heating and aerodynamic forces cause extremely high temperatures, severe thermal gradients, and high stresses. Stagnation regions, such as wing and tail leading edges and nose caps, are critical design areas. These regions experience the highest thermal gradients and mechanical stresses compared with other vehicle components
Gas turbine engine components—particularly stator and rotor blades—also experience extremely high mechanical and/or thermal loading. In general, a gas turbine engine includes, in sequential order, a compressor section, a combustion chamber, and a turbine section. Incoming air is highly compressed in the compressor section by an alternating series of rotating and stationary bladed disks; mixed with fuel and ignited in the combustion chamber; and then exhausted out of the engine through the turbine section, which also includes an alternating series of rotating and stationary disks. The engine may further include a fan in front of the compressor, which fan helps draw air into the engine. Because the various rotating components spin at such at high rotational velocities, their blades are subjected to very large, radially outwardly directed tensile loads. Additionally, the blades are often impacted by solid objects (e.g., birds) that are drawn into the engine, and therefore they must be able to withstand transient dynamic impact loading as well.
Still further, the blades—particularly those in the turbine section—may be subjected to temperatures on the order of 1000° C. to 1500° C. Therefore, they are usually made from highly creep resistant metallic alloys (so-called superalloys). Additionally, as jet engines have been designed to operate at higher and higher temperatures, it has become necessary to cool the blades and other components in some fashion and to limit the thermal flux that enters the various components through the use of thermal barrier coatings (TBC's). Such coatings, however, are not perfectly reliable in all cases, so the engine components must be able to continue functioning even after a portion of the TBC spalls.
Moreover, the hollow structure of hot engine section turbine blades is used to introduce cooling air into the interior of the blade. It is then allowed it to exit the blade/vane through an array of small holes, thus creating a cooling film on the blade surface. This enables an increase in the operating temperature of the engine while maintaining the temperature of the blade material below that which results in service failure (by oxidation, hot corrosion or creep/fatigue), even when TBC spalling occurs. Oxidation- and hot corrosion-resistant coatings are beginning to be widely used to slow the degradation of blades and other hot engine section components in gas turbine engines. The thermally insulating ceramic coatings applied on top of these layers reduce the blade metal surface temperature and therefore the rate of degradation during service.
In addition to these heat and strength considerations, it is also important that aerospace components be as light as possible because a heavier a vehicle has higher fuel costs associated with it. Additionally, heavier rotating engine components have higher rotational inertia and are therefore less responsive (i.e., they take longer to spool up or spool down) than lighter components.
Thus, these considerations present intricate design challenges to an aerospace engineer.